The
butterfly valve is a valve that uses a circular butterfly plate as an opening and closing part and rotates with the stem to open, close and adjust the fluid channel. The butterfly plate of the butterfly valve is installed in the diameter direction of the pipe. In the cylindrical channel of the butterfly valve body, the disc-shaped butterfly plate rotates around the axis. The rotation angle is from 0 degree to 90 degree. The valve is fully open when it is rotated to 90 degree.
The development history of butterfly valves
In the 1930s, the butterfly valve was invented in the United States, which was introduced into Japan in the 1950s. It was widely used in Japan in the 1960s, while it was popularized in our country after the 70s. At present, the butterfly valve above DN300 mm has gradually replaced gate valves in the world. Compared with the gate valve, the
butterfly valve has a short opening and closing time, small operating moments, small installation space and light weight. Take DN1000 as an example, the butterfly valve is about 2T, while the gate valve is about 3.5T. The butterfly valve is easy to be combined with various driving devices and has good durability and reliability. The disadvantage of rubber seal butterfly valves is that improper use will produce cavitation when used for throttling, so the rubber seat peeling, damage and other situations occur. For this reason, the metal-sealed butterfly valve is developed in the international community with reduced cavitation area. In recent years, the metal-sealed butterfly valve was developed in our country. In recent years, the comb-shaped butterfly valve, which withstands cavitation, low vibration and low noise, was developed in Japan.
Under normal circumstances, general sealing seat life is 15 to 20 years if it is rubber, and it is 80 to 90 years if it is metal. However, how to choose correctly should be based on the requirements of working conditions.
The relationship between the opening and the flow rate of butterfly valves, a linear proportional changes. If we used to control the flow, the flow characteristics and pipe flow resistance are also closely related. If the pipeline loss coefficient is different, the valve flow will be very different. If the valve is in the state of a large throttling range, the back of the valve plate is prone to cavitation. There is the possibility of damage to the valve.
When the butterfly valve is open, the two sides are in completely different states. The butterfly plate on one side of the front end moves downstream the water direction. It moves countercurrent in the water direction on the other side. Therefore, one side of the valve body and valve plate form the nozzle opening. On the other side, it is similar to throttle aperture openings. The speed on the nozzle side is quicker than that of the throttling velocities. The valve on the throttle side will produce negative pressure below, where rubber seals often fall off.
The butterfly valve and the butterfly rod have no self-locking capability. In order to locate the butterfly plate, the worm gear reducer should be installed on the valve stem. The use of a worm gear reducer not only can make the butterfly plate with self-locking ability, so that the butterfly plate stopped in any position, but also can improve the operating performance of the valve.
The operation torque of butterfly valves is different due to the different opening degrees, and opening and closing directions of valves. In horizontal butterfly valves, especially large-diameter butterfly valves, the water head difference can not be ignored due to the water depth and the torque generated by the valve shaft. In addition, when the elbow is installed on the inlet side of the valve, the deflection will be formed and the torque will increase. When the valve is in the middle of the opening, the operating mechanism needs to be self-locked due to the water flow moment.
The structure characteristics of butterfly valves
The butterfly valve structure is simple. It is only composed of a few parts. The volume is small. The weight is light, and the installation size is small. The driving torque is small, too. Moreover, the operation is simple and rapid. It only needs to rotate 90 degree to quickly open and close. It also has a good flow regulation function and closed sealing characteristics. The butterfly valve is the dominant form of the valve in large and medium diameter, low pressure in the field of use. When the butterfly valve is in the fully open position, the thickness of the butterfly plate is the only resistance. The pressure drop generated by the valve is small when the medium flows through the valve body. It has better flow control characteristics. The butterfly valve has two types of metal seals. The elastic seal valve and sealing ring can be mounted on the body or attached to the butterfly plate around. The valve with a metal seal is generally longer than the valve with an elastic seal, but it is difficult to achieve a complete seal. Metal seals can adapt to higher working temperatures, and elastic seals have defects limited by temperature. If a butterfly valve is required to be used as a flow control, it is important to correctly select the valve size and type. The structure principle of butterfly valves is especially suitable for the production of large-diameter valves. The butterfly valve is not only widely used in petroleum, gas, chemical, water treatment and other general industries, but also used in the cooling water system of thermal power stations. The commonly used butterfly valve has two kinds of butterfly valves and flange butterfly valves. The wafer butterfly valve is connected between the two pipe flanges with a double bolt. The flange butterfly valve is a valve with a flange, with bolts on both ends of the valve flange connected to the pipe flange. The strength performance of the valve refers to the ability of the valve to withstand medium pressure. Valves are mechanical products that withstand internal pressure. Therefore, we have sufficient strength and stiffness to ensure long-term use without rupture or deformation.
With the application of anticorrosive synthetic rubber and teflon, the performance of butterfly valves can be improved and meet different working conditions. In recent decades, the metal seal butterfly valve has developed rapidly. With the application of high-temperature resistance, low-temperature resistance, strong corrosion resistance, strong erosion resistance and high strength alloy materials in the butterfly valve. The metal seal butterfly valve has been widely used in high temperature, low temperature, strong erosion and other working conditions. It partially replaces the globe valve, gate valve and ball valve.
The Butterfly valve has the characteristics of a simple structure, small volume, light weight, material consumption, small installation size, quick switch, 90 degree reciprocating rotation, and small driving torque. It is used to cut off, put on and adjust the medium in the pipeline. It has good fluid control characteristics and close sealing performance.
The butterfly valve delivers mud with minimal fluid accumulation at the pipe opening. Good sealing can be achieved at low pressure. The adjustment performance is good. The design of the flow line of the butterfly plate makes the loss of fluid resistance small, so it can be said that it is an energy-saving product. The valve stem is through rod structure. After quenching and tempering treatment, it has good comprehensive mechanical properties, corrosion resistance and abrasion resistance. The butterfly valve opens and closes when the stem is only for rotating movement without lifting operation. The stem packing is not easy to destroy, and it has a reliable seal. Fixed with the butterfly plate cone pin, the outstretched end is designed to prevent the blow out of the valve stem when the connection is between the stem. The butterfly plate is broken unexpectedly.
The connection modes include flange connection, clip connection, butt welding connection and lug clip connection. Drive forms are manual, worm gear drive, electric, pneumatic, hydraulic, electro-hydraulic linkage and other actuators, which can achieve remote control and automatic operation.
The disadvantages of the butterfly valve are as follows:
1. The use pressure and working temperature range are small.
2. The sealing is poor.
